DNA ligases can join polynucleotides together, for example by catalyzing the formation of a phosphodiester bond at single- or double-stranded breaks on duplex DNA. Ligases can be sensitive to the degree of hybridization between opposing nucleic acid strands in a duplex. For example, successful ligation can occur less frequently (or not at all) where a strand to be ligated to an adjacent strand is in a duplex and is not complementary to its opposing strand in the duplex. In some cases a single nucleotide mismatch between strands in a duplex can significantly impair or prevent ligation. The capacity of ligases for discrimination based on hybridization, including single nucleotide discrimination, has led to the development of ligase-mediated detection techniques (e.g., Landegren, U., Bioessays, 15(11):761-765 (1993), and Barany, PNAS USA, 88(1):189-193 (1991)). Ligase-based linear signal amplification known as LDR (i.e., ligase detection reaction), combined with PCR (i.e., polymerase chain reaction)-based gene specific target amplification, has been proven to be a useful tool in cancer and disease gene mutation detection. PCR/LDR techniques typically rely on two properties of a DNA ligase: (i) specificity, and (ii) thermostability.